On Wed, Oct 02, 2013 at 12:33:33PM +0200, Jiri Pirko wrote:

Wed, Oct 02, 2013 at 01:25:34AM CEST, hannes@stressinduktion.org wrote:

quoted

On Tue, Oct 01, 2013 at 11:47:21PM +0200, Hannes Frederic Sowa wrote:

quoted

The strange thing is that if I don't do the IPV6_MTU setsockopt I don't
get an oops.

This is incorrect, it just depends on the size of the writes and on the
interface mtu.

quoted

IPv4 seems to work without problems, too.

I also get kernel oopses from IPv4 now, too.

I'm not able to trigger this with ipv4. Can you please send strace
output for this as well?

I used this snippet on loopback with UFO enabled and lo mtu 1280.

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <linux/udp.h>
#include <stdio.h>

int test(int mtu)
{
        int fd;
        const int one = 1;
        const int off = 0;
        struct sockaddr_in addr = {.sin_family = AF_INET, .sin_port = htons(53) };
        unsigned char buffer[3701];

        inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr);

        fd = socket(AF_INET, SOCK_DGRAM, 0);
        connect(fd, (struct sockaddr *) &addr, sizeof(addr));

        setsockopt(fd, IPPROTO_UDP, UDP_CORK, &one, sizeof(one));

        write(fd, " ", 1);
        write(fd, buffer, sizeof(buffer));
        write(fd, " ", 1);

        setsockopt(fd, IPPROTO_UDP, UDP_CORK, &off, sizeof(off));

        close(fd);
}

int main() {
        test(1280);
}

Greetings,

  Hannes